Control means for hydraulic elevators



W. STELZER Nimm Il li Ii Il :a l la yNTOR.

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nited States The invention relates to control means for hydraulic elevators or more particularly to a hydraulic valve for governing the speed and force of hydraulic elevators, .and incorporates certain features of a device disclosed in my copending application Serial No. 427,753 led May 5, 1954.

The improved device lends itself ideally for use with home elevators, especially inclined elevators having open platforms running along stairways, where the customary safety devices used in connection with modern elevators 'would either be impractical or prohibitive in cos-t. It is particularly suited in applications where the minimum amount of structure should be exposed on the stairway, necessitating a remote power cluster consisting of an electric motor, pump, fluid reservoir and control valves.

The object of the invention is to provide control means with which the lifting force of the elevator is automatically adjusted to be only slightly greater than the resistance imposed by the loa-d, so that if any additional acciden-tal resista-nce is introduced after the start of the elevator, the platform is arrested.

Another object is to provide a hydraulic pump, a hydraulic lifting motor to lift the platform, a solenoid operated valve to direct fluid from the pump to the lifting motor, a damper to retard the movement of the valve, and a pressure relief valve that is automatically set Ithrough :the .action of the solenoid operated valve when the upward Vtravel of the elevator is' started from any position so that `the hydraulic pressure delivered by the pu-mp is relieved whenever it exceeds a certain pressure above the pressure that existe-d at the start 4of lthe upward travel of the elevator.

Another object is to include a regulating valve to automatically control the ydescent of the elevator platform, making it possible that either the speed of downward travel is constant regardless of load, or that the platform -descends fmter with a lighter load and more slowly with a heavier load. p

A further object is to coordinate the parts of the device in such a manner that the pump always starts without load, and that the hydraulic lift motor is arrested and hydraulically held in the upper position without leakage of fluid.

v Other objects and advantages of this invention will be apparent from the following description considered in connection with the accompanying drawing submitted for the purpose of illustration and not to define the scope of the invention, reference being had for that purpose to the subjoined claims. In the drawing, wherein similar reference characters refer to similar parts:

. Fig. l is a diagram of vthe novel control system including an elevational cross-section of the valve unit; and

Fig. 2, .a fragmentary View of the valve unit similar to Fig. l', but showing the valve plunger inthe power applied position.

Before explaining the present invention in detail it is to be' understood that the invention is not limited in its application to the details of construction and arrangement arent 2,782,599 Patented Feb. 26,

of elements illustrated in the `accompanying drawing, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also itis to be understood that phraseology and terminology employed herein is for the purpose of description and not limitation.

Describing the invention now in detail, the system consists of a constant delivery hydraulic pump 1 driven by an electric `moto-r 2 to transmit hydraulic uid from a reservoir 3 through a pipe 4, a valve unit indicated in its entirety by numeral 5, and pipe 6 to a hydraulic fluid lift motor 7 which drives the platform of the elevator in the usual manner. The valve unit is actuated by solenoids 3 and 9 energized simultaneously with motor 2 by current from line 1i) when one or the other of switches 11 and 12 are closed. The electric diagram only suggests the power circuit and does not show the usual control means comprising push buttons, interlocks, limit switches etc., since these form no part of ythe invention.

Valve unit 5 comprises .a body 14 having `a bore 15 in which slides a valve plunger 16 secured to a stem 17 operatively connected to solenoids 3 and 9 by means of a bell crank 18 pivoted at 19, 20 indicating a solenoid plunger attracted by one or the other of lthe solenoids. Elements 18, 19 and 20 are shown diagrammatically in order not to encumber the drawing; ordinarily, the solenoids may actuate plunger 17 directly without the interposition of linkage. The valve unit 5 is also shown diagrammatically -to place all elements in one plane for better illustration. Valve plunger 16 is provided with leakproof sliding seals 2l, 22, and 23, which may be of the O-ring type or moulded directly to the plunger. An internal groove 24 in bore 15 communicates with pipe 6. Another internal groove 25 of extremely small size communicates through passage 26 and pipe line 27 with a chamber 2S of a pres'- sure relief valve which will be described later. Plunger 16 has a central passage 3i) connected through a hole 31 with an annular chamber 32 and via hole 33 and throttling valve 34 to sump 3. The valve plunger is shown in the neutral or oft position where the fluid in pipe 6 is sealed against pump 1 and reservoir 3 by seal 23 and edge 35 of plunger 16. Edge 35 is not a perfect seal, but the fluid tha-t passes by is stopped by seal 21 and by a check valve 36 housed in chamber 37 which is always in communication with the annular chamber 3S surrounding valve plunger 16. A fitting 40 inserted into a bore 41 and having a central hole 42 serves as the seat for check valve 36. A packing 43 seals the tting against bore 41, so that with the action of check valve 36 no fluid can ever return from chambers 37 or 38 to pump 1 via pipe 4. Plunger 16 is capable of sliding movement to the left or right equal to the distance between a damper piston 44 and a plate 45 housed within a borre 46 of a' cylinder 47 secured to body 14. The piston 44 and plate 45 are urged apart by .a centering spring 48. This centering spring serves to bias the valve plunger into the neutral or off position, as shown. Piston 44 has a small orifice 50 to permit the slow passage of fluid from within bore 46 when the valve plunger is ymoved to the right to cause the elevator platform to ascend. Both piston 44 and plate 45 are slideable on the smaller portion of stem 17 and abut against faces 51 and 52 respectively, with the result that when the plunger 16 is moved to the right, piston 44 is picked up to travel in unison with plunger 15, while plate 45 remains seated at the bottom or bore 46, and when plunger 16 is moved to the left, plate 45 is picked up by face 52 of stem 17, while piston 44 remains in the position shown.

A bore 54 concentric with bore 15 is provided at one end of body 14 and accommodates a slidable piston 55 having a seal 56 dividing bore 54 into chambers 57 and 2S, the latter being closed olf by an end plug 5S having a central bore 60 in which'slides a piston 61 provided with a seal 62 and urged towards piston 55 by a spring 63, thereby tending to reduce the volume of chamber 28. Spring 63 is shown in the extended position where its force is zero. Piston 55 has a valve head 64 closing olf an exhaust outlet 65 yand controlling communication between chamber 57-which is connected to the pump through passage 66 in body 14 and holes 67 in fitting 40-end passage 30 which leads to the reservoir. A spring tended check valve 68 permits flow of lluid lfrom chamber 28 to chamber 57 through passages 70 and 71 but checks it in the opposite direction. A small stem 72 containing passage 70 is tightly pressed into piston 55 and slidably extends into a central bore in piston 61 to serve as a guide for both pistons 55 and 61. There is sulicient clearance around stem 72 that the fluid near the bottom of the central bore of piston 61 can escape into chamber 28 when pistons 55 and 61 move towards each other.

The hydraulic lifting motor 7 preferably consists of a cylinder 74, a plunger 75 sliding through a sealing sleeve 76 to lift the platform of the elevator, which is not shown since it forms no part of this invention. The uid which may leak past seal 76 is carried away by pipe 77 to sump 3. The bottom of the plunger 75 ts into a cavity when it nears the bottom of its stroke to trap the fluid so as to provide a cushioning effect, a restricted passage 78 permitting descent at reduced speed. A leakproof seal 80 near the lower end of plunger 75 and entering sleeve 76 at the end of the upward stroke serves to prevent gradual descent of the plunger when in the top position. In the embodiment shown, power is used for the ascent only; for the descent the weight of the descending elements forces the uid from cylinder 74 into reservoir 3 via throttling valve 34 when valve plunger 16 is moved to the left. Valve 34 comprises a body 81 screwed into bore 82 in a boss 83 extending downwardly from the main portion of body 14. The upper part of body 81 forms a cylinder 84 in which slides a piston 85 having a stem 86 connected with an impeller 87 urged upwardly by a spring 88 seated on la perforated disc 90 held by an internal retainer ring 91, an extension rod 92 sliding through disc 90 to act as a guide in a central and vertical movement. Piston 85 is capable of restricting the passage of fluid downwardly into the reservoir by partly closing off slots 93. A small hole 94 extends lengthwise through piston 85, and another hole 95 passes through the head of cylinder 84.

Describing now the operation, and assuming that the elevator is in the bottom position and at rest, with the elements in the position shown in Fig. l, closing of switch 11 causes energization of motor 2 and solenoid 9, the latter moving valve plunger 16 towards the right. Due to the action of damper piston 44, the movement is slow enough to give the electric motor 2 time to start before seal 23 passes groove 25, whereby the hydraulic pressure in chamber 28 is atmospheric, as in reservoir 3, so that the slightest pressure generated by pump 1 opens relief valve 64 to short-circuit the ow of Huid from the pump through passage 66, hole 65, passages 30 and 33, through throttling valve 34 into the reservoir. Spring 88 is of such strength that the flow from the pump is not able to close regulating valve 34. After seal 23 has passed groove 25, the hydraulic pressure generated by pump 1 and communicated past check valve 36 and edge 35 into pipe 6 is also transmitted to chamber 28, since the valve plunger intermediate seals 22 and 23 is smaller in diameter than for instance between seal 22 and edge 35, to permit a suthcient passage of fluid from the pump through groove 25, hole 26, and pipe 27 into chamber 28 to seat valve 64 and push piston 61 to the left to load spring 63. After closure of valve 64 the discharge of pump 1 is transmitted to the motor mechanism 7 to lift plunger 75 and the elevator platform. After plunger 16 has moved the full distance to the right where piston 44 rests against plate 45, groove 25 is completely shut 0E from theV pump pressure, as illustrated in Fig. 2. Accordingly, the uid in chamber 28 is now locked and spring 63 loaded with a force representing the pressure required at the beginning ofthe stroke to lift plunger 75. Due to the acceleration at the start, the hydraulic pressure is likely to be somewhat higher than after acceleration; therefore, when the pressure is reduced in cylinder 74 and consequently in the pump, the pressure in chamber 28 is relieved equally through check valve 68. It is therefore desirable that the spring which urges check valve 68 to be closed is aslight as possible so that the pressure in chamber 28 is practically the same as the pressure required to lift plunger 75 after acceleration has taken place. If an `obstacle is accidentally placed in the path of the platform, the ascent is immediately interrupted because the Huid delivered by pump 1, being under higher pressure resulting from meeting the obstacle than that existing in chamber 28, is by-passed through passage 66 and exhaust outlet 65 to the reservoir. The additional load or resistance required to stop the ascending platform and plunger 75 depends on the area of exhaust outlet 65 relative to the area of bore 54. The greater the ratio between the two is, the less additional load or resistance is required to stop the elevator. When plunger 75 nears the top portion, switch 11 is opened to deenergize the pump and solenoid 9, causing a gradual slow-down through the retarded action of valve plunger 16 which is returned to the neutral by the force of spring 48. The exact stop may be provided by a shock absorbing bumper arresting the plunger or platform, since only a small force is required to do this, as explained above. In the top position of the plunger, seal is located within sleeve 76, and with the valve plunger 16 in the neutral position illustrated in Fig. 1, piston 7S is hydraulically held, making a latch or other holding device unnecessary.

To cause plunger 75 to descend, switch 12 is closed to energize solenoid 8 which moves plunger 16 to the left. In this movement no damping action takes place since piston 44 stands still and spring 48 is compressed by plate 45. When plunger 16 is fully moved to the left, communication is established between groove 24 and chamber 32 so that the iluid `displaced by the descending plunger 75 can return to reservoir 3. It is apparent that ordinarily plunger 75 would descend rapidly with a heavy load and slowly with a light load or no load. However, it is desirable that exactly the opposite takes place, so that the empty platform can be returned to the lower station with increased speed. As the hydraulic Huid passes through slots 93 and impinges on impeller 87 to be deileeted radially, the reaction from the mass lcauses impeller 87 to move downwardly against the action of spring 88 to pull piston 85 down to partially close slots 93 and thereby increase the resistance to reduce the downward velocity of the hydraulic Huid and consequently the speed of descent of plunger 75. Hole 95 permits the hydraulic fluid above slots 93 to act on piston 85. The restricted hole 94 in piston 85 prevents an excessive build-up of pressure acting on piston 85.

Since at low pressures, when plunger 75 descends with little or no load, the pressure difference above and below slots 93 is very small, the pressure acting down on piston is negligible. On the other hand, when the load acting on the descending plunger 75 is heavy and slots 93 are partly closed otf, the pressure difference is greater and the pressure acting on piston 85 is increased. The restricted bleeder hole 94 prevents an excessive buildup of pressure above piston 85 when the ow of fluid is throttled very much. Hole 94 could be eliminated if the diameter of piston 85 were reduced so that the maximum force on it would never be sufficient to completely compress spring 88, but since piston 85 also acts as a throttle in cooperation with slots 93, a certain minimum size is required to permit the passage of fluid when the pressure is low. The desired action of the throttling valve can be obtained by the proper selection of spring 88. and the relative sizes of holes 94 and 95. Thus if hole 94 areas-e6 Y is reduced relative to hole 95, the pressure above piston 85 is increased so that a heavy load has the tendency to descend 'more slowly than a light load. By selecting a spring 88 with a high rate of increase of force, the spring has a tendency to counteract the efiect of piston 85 to speed up the descent of a heavy load. The object of course is to prevent the unbalance of the throttle valve' where the pressure of the fluid on piston 85 would reduce the opening through slots 93 which in turn would increase the differential pressure to increase the downward force of piston S5 until the valve would be completely throttled where only very little fluid would pass and the elevator platform would not descend as desired. This is prevented by the action of spring 88, the reduced force on impeller 87, and the reduction in pressure due to bleeder hole 94. When plunger 75 nears the bottom of its stroke, its lower end enters the cavity in cylinder 74 to trap the fluid therein which must escape through the small orifice 78 to provide a cushioning eiect. When switch 12 is opened again, valve plunger 16 returns to neutral by virtue of spring 48 to again assume the position shown in Fig. l.

Pump 1, motor 2, snmp 3, valve 5 and solenoids 8 and 9 may be built integral as one unit, with throttling valve 34 preferably extending below the fluid level of reservoir 3.

Having thus described my invention, I claim:

l. In a hydraulic system including a power driven pump, a hydraulic lluid reservoir connected to the intake of said pump, a hydraulic motor mechanism adapted to receive tluid from said pump to do work, a control valve comprising a body and movable element to control the transmission of hydraulic iluid discharged by said pump, a relief valve to open a path for the lluid discharged by said pump to return to said reservoir, means responsive to the hydraulic pressure generated by said pump to open said relief valve, a chamber containing hydraulic Huid, resilient means tending to resist the expansion of said chamber with a progressively increasing force, means responsive to the hydraulic pressure in said chamber to urge to close said relief valve, and means to bias said control valve to assume a neutral position where said hydraulic motor mechanism is shut ofi" from said pump and said reservoir, and where said chamber is in communication wi-th said reservoir to be relieved of pressure, said control valve being so constructed that when said plunger of said control valve is moved a certain distance in one direction the hydrau-lic pressure of the uid discharged by said pump is communicated to said chamber as well as to said hydraulic motor mechanism and the communication between said chamber and said reservoir is cut ott", and when said plunger is moved further fthe communication between said pump and said chamber is cut oif so that the hydraulic lfluid in said chamber is locked and held under pressure by said resilient means.

2. The combination as claimed in claim 1, and means to reduce the hydraulic pressure in said chamber when said hydraulic pressure is greater than the pressure produced by said pump.

3. The combination as claimed in claim l, and a check valve between said control valve and said pump to check the flow of iluid from said control valve to the discharge side of said pump.

4. The construction as claimed in claim l and a damper to retard the movement of said movable element when moved to direct hydraulic uid from said pump to said motor mechanism to prolong the interval of time before said chamber is cut oi from communication with said discharge of said pump.

5. The construction as claimed in claim l, and means to actuate said movable element of said control valve.

6. In a hydraulic system including a power driven pump, a hydraulic fluid reservoir connected to the intake of said pump, a hydraulic motor mechanism adapted to receive fluid from said pump to do work, a control valve comprising a body and a movable element to control the transmission of hydraulic fluid discharged by said pump, a relief valve adapted to relieve the pressure generated by said pump, means responsive to the hydraulic pressure generated by said pump to urge said relief valve to open, an expansible chamber containing hydraulic uid, resilient means tending to resist the expansion of said chamber with a progressively increasing force, and means responsive to the hydraulic pressure in said expansible chamber Ito urge to close said relief valve, said control valve being so constructed that when said movable element is in a neutral position said hydraulic motor mechanism is cut off from said pump and said expansible chamber is in communication with said reservoir to be relieved of pressure, and that while said movable element is moved into a power applying position said control valve causes communication between said expansible chamber and the discharge of said pump, and where in a fully applied position of said control valve said expansible chamber is again cut ot from said discharge of said pump.

7. In a hydraulic system having a power driven pump, a hydraulic lluid reservoir connected to the intake of said pump, a hydraulic motor mechanism adapted to receive fluid under pressure from said pump to do work, in combination, a relief valve mechanism comprising a cylinder having an end wall with a relatively small exhaust outlet in communication with said reservoir forming a valve seat, a piston sliding in said cylinder and carrying a valve head to engage said valve seat, said piston dividing said cylinder into a rst chamber and a second chamber, said iirst chamber being adjacent said outlet and in communication with the discharge of said pump, a second piston entering into said second chamber, resilient means resisting the ejection of said second piston by the hydraulic pressure in said second chamber with progressively increasing force, and valve means to control the transmission of fluid between said pump and said motor mechanism, said valve means being adapted to selectively connect said second chamber with said reservoir and said discharge of said pump, and to cut oii the connection of said second chamber completely when said motor mechanism is in operation.

The construction as claimed in claim 7, and a check valve between said first chamber and said second chamber to facilitate the relief of pressure from said second chamber to said tirst chamber and to check the ow in the opposite direction.

9. The construction as claimed in claim 7, where said second piston is smaller in diameter than said rst mentioned piston.

l0. The construction as claimed in claim 6, where said control valve is adapted to relieve the iluid from said motor mechanism to return said uid to said reservoir, and a throttling valve to control the speed of return of iiuid to said reservoir.

1l.. The construction as `claimed 4in claim 10, said throttling valve comprising a throttle through which the hydraulic fluid returning from said motor mechanism must pass, resilient means tending to keep said throttle open to oder a minimum resistance to the flow of hydraulic fluid returning from said motor mechanism, an impeller arranged to deect the returning uid from its path after havingr passed said throttle, means to transmit the force of reaction obtained by said impeller to close said throttle, and means responsive to the pressure difference caused by said throttle to urge said throttle to close, said throttle, said resilient means, and said means responsive to the pressure difference caused by said throttle to urge said throttle to close, said throttle, said resilient means, `and said means responsive to the pressure difference being so proportioned as to cause a faster descent of a light load and a relatively slower descent for a heavy load.

l2. In a hydraulic system includinga power driven pump, a hydraulic motor mechanism to do work, and

uid. pressure transmitting means to transmit uid from saidpump to said motor mechanism, in combination, vaive means to control the transmission of iuid from said pump to said motor mechanism, a relief valve to relieve the pressure generated by said pump, means responsive to the hydraulic pressure generated by said pump to urge said relief valve to Open, an expansible chamber adapted to receive hydraulic Huid, resilient means resisting the expansion of said chamber with a progressively increasing force, means responsive to the hydraulic pressure in said expansible chamber to urge said relief valve to close, second valve means to first transmit hydraulic uid from said pump to said expansible chamber and to subsequently shut off the transmission of uid to saidvexpansible chamsaid expansible chamber to the discharge side of saidy pump when the hydraulic pressure in said chamber is" greater than the pressure generated by said pump.

lReferences Cited in the file of this patent UNITED STATES PATENTS 2,280,291 Jaseph Apr. 2l, 1942 2,366,382 Bl'tOn et al Jan. 2, 1945 

